Preheat oven to 400 degrees Fahrenheit.
In a large skillet melt two tablespoons of butter on high heat. Add in the carrots, parsnips, celery, and onion. Mix well and add in the turkey broth. Cook on medium-high heat with lid on for 10 minutes, Stirring occasionally.
Once the veggies are cooked add in the diced mushrooms, green peas, parsley, poultry seasoning, black pepper and salt. Mix well and add in the leftover turkey gravy.
In a small bowl, combine the milk and cornstarch until well blended. Pour the mix into the pot and mix until well incorporated. Cook on medium heat for 5 minutes until the mixture thickens. *If it's still not thick cook a few more minutes. Add in the turkey and mix well. Remove from heat and set to the side.
Roll out one of the pie crust (make sure you let your pie crust sit at room temperature for at least 15 minutes). Place in a pie dish and crimp edges. Poke the bottom of the pie crust with the tines of a fork (a few times). Pre-bake crust for 10 minutes.
Remove crust from oven, pour the chicken pot pie filling into the pre-baked crust. Roll out the second pie crust. Place on top of the pot pie. Carefully crimp edges to secure pie crust. Cut a few slits in the top of the pie crust. Brush the top of the pie crust with a beaten egg.
Bake for 30 minutes until pot pie is golden brown. Slice and serve immediately upon being cooked and place on a bed of spinach if you'd like!